Wrinkle-free metal shells



May 1966 R. J. OBRIEN ETAL 3,250,419

WRINKLE-FREE METAL SHELLS Original Filed Dec. 15, 1959 4 Sheets$heet l fF 07/??? W I72 we 22 30 2 5 fiaeri J 0275670 Q4 Gowam M ZJZ y 1966 R. J.O'BRIEN ETAL 3,250,419

WR I NKLE-FREE METAL SHELLS Original Filed Dec. 15, 1959 4 Sheeis-Sheet2 United States Patent 3,250,419 WRlNKLE-FREE METAL SHELLS Robert J.OBrien, Evanston, and Gordon A. Vold, Palatine, Ill., assignors toEkco-Alcoa Containers, Inc., a corporation of Illinois Originalapplication Dec. 15, 1959, Ser. No. 859,706, now Patent No. 3,147,724,dated Sept. 8, 1954. Divided and this application Jan. 14, 1964, Ser.No. 347,083

1 Claim. (Cl. 2201) This is a division of application Serial No.859,706, filed December 15, 1959, now Patent No. 3,147,724.

This invention relates to thin walled metal shells and particularly towrinkle-free shells of this character and to the production thereof fromthin metal sheets.

Thin walled metal shells are customarily formed by drawing processesfrom flat sheet metal blanks, and in the drawing process the edges ofthe blank are clamped between a die face and a yieldingly pressed blankholder so that as the central portions of the blank are forced into thedie cavity by a punch, the metal of the blank is drawn or stretched sothere is a marked thinning of the metal as the drawing operationproceeds. The border portion of the blank that has been clamped duringsuch a conventional drawing operation becomes a border flange about theupper edge of the side walls of the completed shell, and as a finaloperation the flange is trimmed.

It has long been recognized that drawing processes have an inherenttendency not only to objectionably stretch and thin the sheet but alsoto produce wrinkles in the sides and flanges of the drawn shells, andwhile the art of producing drawn metal shells has been widely used andhighly developed, the problem of eliminating wrinkles in the sides andflanges of the finished shell has never been satisfactorily solved inrespect to many forms of shells and in respect to many kinds andthicknesses of metal.

It is, therefore, the primary object of this invention to provide a newand improved method of producing thin Walled metal shells from flatsheet metal blanks, and another and related object is to provide such anovel process which avoids stretching and thinning of the metal of theblank, and through the use of which wrinkle-free shells or containersmay be produced from thin metal sheets such as aluminum foil.

According to conventional drawing practice the sheet metal blank is putin position across a die cavity and is held in place against the dieface by a yielding blank holder or pressure pad through which a punch ismoved to engage the sheet and force the same into the die cavity, and asthe punch enters the die, the border portion of the blank, that is heldby yielding clamping pressure between the die face and the pressure pad,is drawn inwardly toward the drawing edge, as for example in theformation of a circular shell, or at the rounded corners of arectangular shell, there must be a progressive reduction in thecircumferential dimension of the diverging portions of the flange asthey approach the drawing edge. In other words, each segmental portionof the border must become narrower as it approaches or is drawn inwardlytoward the drawing edge, and this produces what may be termedcircumferentially acting compressive forces in such border which tend toproduce radially extending waves or wrinkles in the border portion ofthe blank.

The tendency that thus exists in conventional drawing operations toproduce radially extending waves in the border portion of the blankvaries of course with the properties of the metal and with the thicknessof the blank, but in any case, such radial waves tend to increase indepth or amplitude as the operation progresses. Thus, where the depth ofthe waves progresses to a point such that the metal is stressed beyondits elastic limit, wrinkles are produced in the flange which mustthereafter be ironed 'ice out by the cooperation of the punch with thewall of the die cavity. The problem of flange wrinkles is encountered inthe drawing of all different types of shells, but with respect to shellshaving taperedsides, further difficulties are met because of theintermediate uncontrolled area presented in the blank between thedrawing edge of the die and the working edge'of the usual forms ofpunch. The present invention is concerned with the elimination of bothflange wrinkles and side wall wrinkles or puckers in shells of the kindusually produced by drawing, so as to enable smooth surfaces to beattained on both the side walls and the flanges of thin walled shellsformed from flat sheet metal blanks.

There are, of course, instances in conventional sheet metal drawingswhere the tendency to produce waves or wrinkles in the flange is notparticularly objectionable because of the nature of the metal or therelatively great thickness of the blank, but with the softer or moreductile metals, and with relatively thin blanks, this tendency towardthe formation of waves or wrinkles in the flange has provided one of themost difficult problems involved in the production of such sheet metalshells. The usual and generally accepted solution 'for correction ofthis problem is to add to or increase the pressure applied by thepressure pad to the border or flange portion of the blank.- This use ofadditional pressure on the border of the blank does not, however,provide a universal answer to the problem that is presented because, asthe thickness of the blank is decreased, the amount of pressure that maybe applied to the border tends to reach a point where the border is heldor retarded to such an extent that exccssive stresses are produced inthe metal and the blank is excessively thinned in the side wall orflange and tends to tear in the side wall portion or at the end edge ofthe punch where the maximum force is applied to the metal. This problemis even more serious where the shell is to be drawn from aluminumbecause the coefficient of friction of aluminum is much higher than thatof the other metals that are conventionally used in drawing operations,and the ductility or plasticity of the metal is substantially greater.Thus, with respect to the drawing of shells from aluminum the usualexpedient of increasing the pressure applied to the flange cannot befollowed, and the pressure must in fact be reduced to such a point thatin the production of tapered wall pans and the like from aluminum foil,the resulting shell does not constitute a drawn shell, but is formedwith wrinkles and folds in both the flange and the side.

The shells that are thus formed from extremely thin aluminum sheetswithin the thickness range of .001 to .005 inch, which is normallyclassified as foil, are in fact shaped by a process that involvesintentional wrinkling and folding of the excess metal that is pulledinwardly from the border portion of the blank, and while such shells orcontainers are satisfactory for many purposes, they involve the use ofmetal in a wasteful manner and result in containers that cannot beproperly cleaned in the removal of the contents thereof. Moreover, thewrinkles in the flanges render it extremely difficult to seal a coveronto the container.

In view of the foregoing it is a further object of the present inventionto enable containers to be made from foil from which the containers aremade.

While the problem of tearing or rupturing the metal blank inconventional drawing operations has been discussed primarily as appliedto extremely thin metal foil blanks, this same problem exists in thickerblanks of other metals including steel, and to guard against suchtearing of the blanks, broad general rules are usually prescribed basedupon or measured by the maximum percentage in diameter reduction thatcan be obtained in a blank in a single draw without danger of tearingthe blank. Thus where relatively deep drawn shells are made it isusually necessary to resort to a series of drawing operations. Thepresent invention, however, is applicable also to thicker metal blanksand by the controlled metal working operation of the present invention,it has been found possible to radically increase the percentage of blankreduction over and above the normal rules or standards that have beenestablished for conventional drawing operations.

The foregoing objectives of the present invention are accomplishedthrough a controlled working of the sheet metal blank in which all ofthe forces that are to be efiective in producing metal flow areappliedto the blank by the forming punch and all resistive forces that areeffective on the border of the blank and which oppose change of form ofthe blank are produced as resultants of the forces initially applied tothe blank by the punch. Hence, the resulting stresses that tend toproduce metal flow in the blank are equalized and are limited tomagnitudes just sufiicient to flow the metal into its new form.

Other and further objects of the present invention will be apparent fromthe following description and claim, and are illustrated in theaccompanying drawings, which, by way of illustration, show a preferredembodiment of the present invention and the principles thereof, and whatis now considered to be the best mode in which to apply theseprinciples. Other embodiments of the invention embodying the same orequivalent principles may be used and structural changes may be made asdesired by those skilled in the art without departing from theinvention.

In the drawings:

FIG. 1 .is a perspective view of a smooth wall, smooth flanged metalfoil container that may be produced under the present invention;

FIG. 2 is a sectional view taken along the line 22 of FIG. 1;

FIG. 3 is a fragmentary plan view taken from the line 3-3 of FIG. 2; I

FIG. 4 is a fragmentary and somewhat schematic vertical sectional viewtaken through a die set and showing the blank at a greatly increasedscale;

FIG. 5 is a bottom perspective that fragmentally shows the relationshipof the parts of the die set to the blank and to each other;

FIG. 6 is a further enlarged portion of FIG. 4 showing the relationshipof the die and the cooperating gauge plate to each other and to theblank;

FIG. 6A is a vertical sectional view taken substantially along the lines6A-6A of FIG. 6;

FIG. 7 is a view similar to FIG. 6 showing the relationship of the blankto the die and gauge plate after the operation has caused thickening inthe flange of the blank;

FIG. 7A is a sectional view taken substantially along the line 7A--7A ofFIG. 7;

FIG. 8 is a diagrammatic view illustrating successive changes in theform of the blank as the operation progresses;

For purposes of disclosure the invention is herein illustrated in FIGS.1 to 11, as applied to the production of a circular tapered wallcontainer that is made from aluminum foil as will be described in detailhereinafter.

The container 20 is pan-like in form and has a bottom wall 120, atapered side wall 220 and a horizontal flange 320 at the upper edge ofthe side wall 220. Under the present invention, the container 20 is madewith smooth surfaces on the side wall 220 and on the flange 320 so thatthe appearance of the container is improved as compared to prior foilcontainers of this form and so that smooth surfaces on the flange 326lend themselves to the application of a sealed covered member as isdesirable in the production of hermetically sealed food packages orcontainers.

The smooth walled, smooth flanged tapered container 2!) is produced frommetal foil through the use of a die set 39 of the inverted type having adie 31 disposed .opposite a cooperating punch 32, and about the punch 32'a gauge plate 33 is provided which has a gauge face or surface 33Fdisposed in opposed relation to the die face 31P of the die 31. The die31 has a tapered die cavity 310 which is connected with the die face bya rounded edge 31E, and the punch 32 has tapered side surfaces 32T thatmerge with the end surface 32E of the punch through a rounded corner32R. The tapered surface 32T, at its larger end, has a rounded surface132R that is adapted for cooperation with the radius 31E as the punchreaches the end of its stroke.

The gauge plate 33 is urged endwise on and with respect to the punch 32by resilient means of any convent-ional kind such as expansive springs34 so thatas the punch approaches the die cavity, the punch and thegauge plate 33 will travel together.

The novel mode of operation The die set 30 as thus described necessarilyresembles a conventional drawing die set, but in such a conventionaldrawing die set, the plate 33 would constitute a pressure pad and wouldengage the border portion of a fiat metal blank 40 so as to press andclamp the same against the die face SIP. Under the present invention,however, it should be noted that the function and operation of the gaugeplate 33 with relation to the die 31 distinguishes in a major andimportant sense from prior practice so that a novel controlled metalflow is attained that prevents wrinkle formation in the shell as it isproduced.

Thus, under the present invention, the approaching movement of the gaugeplate 33 with respect to the die face 31 is limited by stop means sothat the relative approaching movement of the gauge plate33 is stoppedin a final working position such that no appreciable clamping force orpressure is exerted initially upon the interposed border portion of theblank 40. Thus, as shown herein, the stop means that are thus effectiveto limit the approaching movement of the gauge plate 33 take the form ofadjustable shims 42. These shims comprise brackets 4313 located on thedie and the gauge plate 33 with aligned vertical stop screws 43Sextended therethrough, and the stop screws 438 of each pair of shims arearranged so that the ends of the stop screws 438 will engage and thusterminate the relative approaching movement of the gauge plate 33.Several sets of shims 42 are of course provided at spaced points aboutthe outer edge of the die set.

Under the present invention the resilient means which apply the pressureto the gauge plate 33 serve only to hold the gauge plate 33 in astationary relation in its final working position as determined by stopmeans 42, and the resilient pressure applied to the gauge plate 33 isselected so as to apply an excess amount of pressure to hold the gaugeplate 33 in such position. The excess of pressure is such that forcescreated by metal flow or deformation of the blank between the die 31 andthe gauge plate 33 in the course of the operation cannot causeseparating movement of the gauge plate and the die. Thus the gauge plate33 and the die face 31F do not function as a clamping or retarding meansas in conventional metal drawing operations, but in contrast serve as aconfining means or chamber of fixed dimensions within which the borderportion of the blank must undergo such metal flow or changes of form asmay be necessary in response to the inward tension resulting from theaction of the punch.

Through the use of means which thus limit the approaching movement ofthe gauge plate and which hold the gauge plate stationary in the workingposition determined by the stop means, the present invention causes anentirely new cooperation of the parts of the die set with each other andwith metal blank, and the net result of this new cooperative action inthe illustrated example is the production of thin Walled shells orcontainers 20 that have smooth tapered side walls and smooth surfacedflanges. The theory and manner of cooperation of the parts of the dieset 30 is illustrated schematically in FIGS. 4 to 11 of the drawings.

Thus, in FIGS. 4 and 5, the thin metal foil blank 40 is shown at ahighly exaggerated scale in position with its border portions locatedbetween the die face 31F and the gauge plate 33 and with the leading endof the punch 32 in engagement with the adjacent face of the fiat blank40. The precise relationship of the die face 311 and the gauge face 33Fto the blank 40 cannot be clearly shown in FIGS. 4 and 5, but in FIGS. 6and 7, this relationship has been shown at a further enlarged scale toillustrate the manner in which the control of the metal stress and flowis attained under the present invention.

It has been pointed out hereinbefore that the approaching movement ofthe gauge plate 33 is so limited by the stop means that in its finalworking position, the gauge plate 33 exerts no appreciable force uponthe border portion of the flat blank, and it should be observed that thespace between the gauge plate 33 and the die face 31? in its finalrelationship should approach as closely as possible to the actualthickness of the metal blank 40 without applying initial pressure to theflat blank. Thus, in a theoretical sense, the final spacing of the gaugeplate 33 from the die face 31P might correspond precisely with thethickness of the metal blank, but as a practical matter, the thicknessof the metal sheet material that is used in the production of suchshells varies within certain relatively small tolerances and provisionmust be made to take care of such variations. Thus, as to metal foil, itis recognized that a tolerance of about five percent must be expectedfor any particular rolled sheet, and in order to take care of plustolerances, the stops or shims 42 are set so that the final spacing ofthe gauge plate 33 from the die face 31P is about five percent greaterthan the specified or nominal thickness of the sheet metal that is to beused.

The action of the apparatus under such a setting of the shims 42 will bediscussed hereinafter, and to facilitate such discussion, attention isdirected to the schematic illustration of FIG. 5. Thus, in FIG. 5, afragmentary bottom perspective view has been shown wherein a pieshapedor segmental portion of the flat blank 40 is disposed between the die 31and the gauge plate 33, and in FIG. 5 the punch 32 is shown at itsinitial point of engagement with the blank 40 opposite the die cavity.It will be apparent that when the punch 32 advances toward and into thedie cavity from the position shown in FIG. 5, the material of the blank4% that is located radially inwardly from the radius 31E will be movedinto the die cavity, and the portion of the blank 40 that is locatedbetween the radius 31B is drawn at an angle into the die cavity so as tohave a radially inward force 45 applied thereto as indicated in FIG. 5.This radially inward force 45 will of course tend to pull the flange orborder portion of the blank in a radially inward direction, and in orderfor the flange portion to move radially inward it is necessary that theflange portion be compressed in a circumferential direction. Thiscircumferential compression may be said to develop circumferentiallyacting forces 46 in the flange areas as indicated in FIG. 5. As a resultof such circumferential forces,

there is an initial tendency for the flange portion to form into radialwaves to the extent that is permitted by the excess space between thedie face 311 and the gauge plate 33, and the space between the gaugeplate 33 and the die face thus acts to limit the depth or amplitude ofany such radial waves that do form, and serves to limit the thickness towhich the flange portion of the blank may expand or thicken by metalflow as a result of the circumferential forces 46. The restrictiveforces that thus limit the maximum thickness of the border portion areindicated at 47 in FIG. 5, and to maintain the desired maximum spacingof the die face and the gauge plate such forces must exceed theseparating forces created by the thickening of the border portions ofthe blank.

In FIGS. 6 and 6A, the blank 4% has been schematically illustrated at agreatly enlarged scale to show the final or fixed gauging position ofthe gauge plate 33 with relation to the die 31, and the illustration hasbeen based on the assumption that the metal thickness that may beexpected is to be within a tolerance of plus or minus five percent.Thus, when the gauge plate 33 and the die-31 have approached to thefinal working position or relation determined by the stop means, thereis a clearance of about .05T with respect to one of the surfaces of theblank, the thickness of the blank 40 being taken as 1.00T. In the eventthat the sheet metal used for the blank 40 has been maintained at asmaller tolerance, the actual final spacing of the pressure pad from thedie face may be correspondingly smaller.

Thus, when the circumferential forces 46 are developed in the flangeportion of the blank as indicated in FIG. 6A, any radial waves 40W thatmay tend to form between the opposed faces of the die 31 and the gaugeplate 33 have their amplitude or depth limited by the space between theblank and the opposed face of the die, and such maximum amplitude orform of such wave 40W for a blank having a thickness of 1.00T isindicated by a dotted line in FIG. 6A. It is important to note that anytendency toward Waviness in the flange portion of the blank is thuslimited to such an extent that the metal of the blank cannot be stressedbeyond its elastic limit, even though such waves reach their maximumdepth or amplitude as indicated in FIG. 6A, and hence, in the subsequentworking of the metal of the blank, these waves may be eliminated byironing or compression to such an extent that they are not appreciablyperceptible to the touch or sight.

The slightly waved .condition that is represented in FIG. 6A by thedotted line showing of a potential radial wave in the border portion ofthe blank, is, however, corrected as the operation progresses, and thiswill become apparent by a comparison of FIGS. 6A and 7A. Thus, as theinward pulling forces 45 cause continued inward radial displacement ofthe border portion of the blank, the circumferential forces 46 have theeffect of causing the border portion of the blank to thicken by reasonof metal flow so that before the operation has progressed to any markedextent the space between the gaugeplate 33 and the die face 31F becomescompletely filled by reason of such thickening of the blank. Thisthickening apparently takes place initially at a radial point relativelyclose to the drawing radius 31E of the die, and progresses outwardly asthe operation is continued so that throughout a substantial portion ofthe operation, the vertical space between the die 31 and the gauge plate33 is completely filled by the metal of the blank.

The metal that is confined in the fixed and accurately defined spacebetween the die 31 and the gauge plate 33 is thus pulled inwardlythrough what amounts to an annular drawing opening 4%, FIGS. 6 and 7,and the slight waves that may have been initially formed in the borderportions of the blank are removed or eliminated by thickening of themetal which presses opposite faces of the blank against the surfaces 31?and 33P with such force that smooth surfaces are formed on the metal ofthis border portion. The pressing of the faces of the blank against thedie face 31 and the gauge plate 33 serves of course to produce africtional retarding action, but since such forces are created by metalflow in the blank itself, such retarding forces do not cause appreciablestretching or thinning of the metal in the walls of the shell that isbeing formed. Near the radius 31E, the metal is smoothed to such adegree that the originally formed waves 40W are substantiallyimperceptible to the sight and are not perceptible to touch. Further outon the flange portion, these original waves 40W are also eliminated butappear to result in what might be termed draw lines that are in someinstances visually perceptible but are practically imperceptible to thetouch.

Thus, when the metal of the blank moves inward over the radius 31E, itis substantially smooth surfaced and free of all wrinkles, but where atapered wall container is being made, the uncontrolled annular area ofthe blank that is located between the radius 31E and the working edge32R of the punch tends to assume a scalloped or puckered appearance asthe drawing operation proceeds, but in this scalloped form, the scallopsor puckers are relatively shallow and are of such a character that inthe final portion of the punch stroke, the scallops or puckers may beentirely eliminated so that the inner and outer surfaces of the sidewall 220 are substantially smooth to the touch and sight. In FIGS. 8 to11 the progressive changes in the form of the blank have beenillustrated and notations have been made upon various steps of FIG. 8 toillustrate the size, position and relationship of the waves in theformation of a shallow pan having a final bottom diameter of 7 /2inches, a depth of 1 /2 inches and a side wall taper of substantiallyten degrees, and the pan being formed from aluminum foil having athickness of .004 inch.

Thus in FIG. 8, and at the top thereof, the blank 40 is illustrated inits fiat or original form. Immediately beneath the blank 40, the formthereof is indicated at 40A where the punch has progressed into the diecavity to a depth of /s inch. As this takes place, substantially uniformradial waves or scallops are formed in the un controlled annular portionof the blank, and these scallops are relatively shallow and at a spacingof from inch to inch. In the border portion of the blank, the inwardradial forces applied as at 46 in FIG. 5, have caused a slightly wavedappearance to be assumed, these waves being in a radial relationship andbeing spaced at approximately inch. In FIG. 8, the next step shows theblank at 40B where the punch has progressed to an /2 inch depth, and inthis instance, the waves or scallops in the uncontrolled portion of theblank become somewhat deeper as indicated, and in the flange or borderport-ion, the thickening of the metal has progressed to such an extentthat the inner portion of the flange is substantially smooth while thewaves in the outer portion thereof have been eliminated or flattened tosome extent by thickening of that portion of the blank.

The blank is next shown in FIG. 8 at 40C in the form that it assumeswhen the punch has progressed to a depth of A; inch, and as indicated bythe legends associated with the blank 40C the side Wall waves and thesurfaces of the flange remain-substantially the same as hereinbeforedescribed with respect to the blank 403.

The blank is next shown in FIG. 8 as indicated at 40D where the punchhas progressed to a 1 inch depth, and in this instance, the entiresurface of the bordering flanges has become smooth although perceptibleradial draw lines may be seen. In the side wall, the radial scallops orwaves have assumed the form shown in FIGS. 9 and 11, FIG. 11 being ahorizontal sectional view at a greatly enlarged scale. It might be notedthat these waves or scallops have I a depth of about inch, and theirspacing is in most instances about 7 inch so that the depth is not morethan one-tenth of the width of the wave or scallop. This relationship issuch that the metal is not stressed beyond the that it assumes when thepunch has progressed to a depth of 1% inches. At this stage in theoperation, the flange remains substantially smooth, while the waves orscallops in the side wall take a somewhat different form orrelationship. Thus, by comparisonof FIG. 10 with FIG. 9 it will be notedthat certain of the scallops or waves in the side wall have remained atsubstantially'the same form and size in which they appear in FIG. 9, butabout every second or third one of the original scallops or waves hasenlarged to a greater extent in an upward direction. At this point inthe formation of the container, the side wall of the punch 32 isextremely close to the side wall scallops or waves, and as the entry ofthe punch progresses, the blank assumes the form shown at 40F in FIG. 8.This view shows the form where the punch has progressed to a depth of 17inches, or in other words to a point where the punch is inch away fromits final or home position. The flange portion of the blank, as shown at49F, still remains in its smooth condition and the cooperation of theside of the punch with the side wall of the die cavity has substantiallyflattened or ironed out the scallops or waves that have been shown inFIG. 10. Then, as the punch moves to its final or home position, theside wall is further ironed so that it becomes substantially smooth tothe touch and the sight, and in this final movement, the bottom wall ofthe shell may be embossed as at to produce the final form of thecontainer that has been indicated at 406 in FIG. 8.

The present invention has been described particularly as applied to theproduction of shells in the form of shallow pans with tapered sides fromthin metal foil such as aluminum foil, but it has been found that thebroad principles of the present invention have highly advantageousapplication to the production of cylindrical shells and to theproduction of shells from other metals and from thicker blanks. Thus asapplied to the making of shells in cylindrical form from steel blanksthe invention has resulted in the attainment of highly improvedperformance, particularly as to the percentage of diameter reductionthat could be obtained. Thus where a 7% inch diameter blank was formedto a shell having 4% inches diameter in cylindrical form it was possibleto obtain a diameter reduction of 36.2 percent without rupture of theblank. Using a 7% inch diameter blank and in making a shell with adiameter of 4- /8 inches, it was possible to obtain a diameter reductionof 39.4 percent. In further work, with a blank having an 8 inch diameterwas used in making a shell with a diameter of 4- /8 inches, and theblank diameter reduction was carried to 42.3 percent. This represents aradical increase over and above conventional drawing operation where theusual recommended diameter reduction would be 32 percent.

In other work on straight side wall containers of a somewhat smallerdrawn diameter, even a greater percentage of blank diameter reductionwas obtained. Thus using a steel blank of 4 /2 inches outer diameter anda shell diameter of 2% inches, the usual recommendation as to themaximum diameter reduction possible in conventional drawing operationsfor a .015 material is 32 percent, but by application of the principlesof the present invention, this diameter reduction was carried up to 47.3percent without causing rupture of the blank.

The present conclusion is that the principles of the present inventionare of greatest value in working with thin gauges of metal, but evenwhere thicker metal sheets are employed, a marked improvement isattained by enabling deeper shells to be made without rupture of themetal. In the employment of the principles of the present invention, thestresses in the blank tending to produce metal flow are equalized andare applied in such a way as to limit these stresses to values justsuflicient to produce the metal flow required to produce the desiredchange of form of the blank. Moreover, the formation of waves in theflange is so controlled as to prevent stressing of the metal beyond itselastic limit, and there is no thinning or folding of the metal of theblank. Hence, any tendency toward weakening or rupturing of the metal isminimized.

From the foregoing description it will be apparent that the presentinvention enables wrinkling of the metal in the formation of shells tobe eliminated in such a way that more perfect shells are produced andthe workability of the metal throughout the operation is preserved. Itwill also be evident that the present invention enables metal foilsheets to be formed into shells without the production of objectionablewrinkles in the sides or flanges thereof, and it will also be evidentthat the present invention enables lighter gauges of metal to beemployed in shell making operations.

It will also be apparent from the foregoing description that the presentinvention, through the elimination of folding or wrinkling in the makingof metal foil dishes and pans, materially reduces the amount of materialrequired, and because the flanges are smooth and wrinkle-free, it ispossible to seal such pans or containers to provide vacuum sealed orhermetically sealed packaging.

Thus while we have illustrated and described a preferred embodiment ofthe invention, it is to be understood that changes and variations may bemade by those skilled in the art without departing from the spirit andscope of the appending claim.

We claim:

A metal foil container formed from a sheet of aluminum foil of athickness ranging between .001 and .005 inch, said container having abottom, a side wall inclined upwardly and outwardly from said bottom, acontinuous flange extending laterally about the upper end of said sidewall disposed parallel with said bottom wall, said side wall andassociated flange being smooth and substantially wrinkle-free, and saidbottom, side wall and flange portions being of a thickness throughout atleast as great as the thickness of the sheet from which the container isformed.

References Cited by the Examiner UNITEDSTATES PATENTS 2,012,529 8/1935Eldredge.

2,649,067 8/1953 Kranenberg 113-44 2,924,369 2/1960 Richter 229 -3.s

2,963,197 12/1960 Lyon 220 74 2,968,270 1/1961 McChesney 113- 43,069,043 12/1962 Bishop 229- 3,098,597 7/1963 Johnson etal. 220-72X3,144,974 8/1964 Eichner et a1. 229-3.5

THERON E. CONDON, Primary Examiner.

R. A. JENSEN, J. R. GARRETT, Assistant Examiners.

